schistosity, mode of foliation that occurs in certain metamorphic rocks as a consequence of the parallel alignment of platy and lath-shaped mineral constituents. It reflects a considerable intensity of metamorphism—i.e., changes resulting from high temperatures, pressures, and deformation.

What causes Schistosity?

schistosity, mode of foliation that occurs in certain metamorphic rocks as a consequence of the parallel alignment of platy and lath-shaped mineral constituents. It reflects a considerable intensity of metamorphism—i.e., changes resulting from high temperatures, pressures, and deformation.

What foliation means?

foliation, planar arrangement of structural or textural features in any rock type but particularly that resulting from the alignment of constituent mineral grains of a metamorphic rock of the regional variety along straight or wavy planes.

What conditions associate in the formation of gneiss metamorphic rock?

Gneiss is a high grade metamorphic rock, meaning that it has been subjected to higher temperatures and pressures than schist. It is formed by the metamorphosis of granite, or sedimentary rock.

Which type of foliated texture occurs when the minerals of a rock segregate forming bands?

Correct! Gneissic foliation is a metamorphic texture in which visible silicate minerals separate into dark and light bands or lineations. These grains tend to be coarse and the bands are often folded and distorted.

What does schistosity look like?

Schist (/ˈʃɪst/ SHIST) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes or plates.

What causes cementation?

cementation, in geology, hardening and welding of clastic sediments (those formed from preexisting rock fragments) by the precipitation of mineral matter in the pore spaces. It is the last stage in the formation of a sedimentary rock.

What are the 4 types of foliation?

The various types of foliated metamorphic rocks, listed in order of the grade or intensity of metamorphism and the type of foliation are slate, phyllite, schist, and gneiss (Figure 7.8).

What is foliation and lineation?

Foliation is the result of the parallel arrangement of (micas, etc.) in a plane perpendicular to the maximum principal applied stress. A lineation is caused by a similar growth of elongate minerals (eg. hornblende) in this plane. Slate, schist, and gneiss are three common foliated metamorphic rocks.

Under what conditions would the highest grade of metamorphic rock be formed?

High-grade metamorphism takes place at temperatures above about 450 ºC. Micas tend to break down. New minerals such as hornblende will form, which is stable at higher temperatures.

How does the banding in gneiss form?

These minerals in the parent rocks are exposed to high amounts of heat and pressure and recrystallized into bands. The process of foliation is what creates these bands in gneiss as the pressure squeezes the elongated or platy crystals into this alignment. The different types of rocks create different kinds of gneiss.

What causes compositional banding?

Compositional banding produced by metamorphic differentiation has long been understood to result from mass transport by either dissolution or diffusion under the influence of a non-hydrostatic stress field.

What texture is biotite?

This rock is mostly composed of creamy-white feldspar and quartz, together with dark minerals, of which the most abundant is the dark mica biotite. The dark minerals are arranged in a streaky banding, giving the rock a gneissic texture.